1. Field of the Invention
The invention is a subsurface explorer (SSX) for exploring beneath the surface of the terrestrial surface of planetary bodies such as the Earth, Mars, or comets.
2. Description of the Prior Art and Related Information
Conventional drilling requires that material be excavated entirely out of a hole, that the hole usually be lined to prevent collapse, and that power be transmitted to the excavation site from the surface by means of a relatively heavy mechanical linkage. The mass (and to a large degree the power and cost) of conventional systems grow proportionally to the desired depth of penetration since heavy mechanical components are distributed along the length of the excavated hole.
Excavation of compacted subsurface material requires energy. While the amount of energy needed to excavate a given volume of subsurface material varies considerably depending on the specific mineral and morphological structure of the medium, as well as the means for excavation, the specific energy requirements for conventional rotary drilling of medium strength rock is about 200 megajoules per cubic meter (Mj/m3). Typical modem rotary drilling equipment is just capable of operating with this level of performance.
Thus, there is a need for a simple, subsurface exploring system and method which requires less energy and support than conventional drilling.
The invention is a subsurface explorer (SSX) for exploring beneath the surface of the terrestrial surface of planetary bodies such as the Earth, Mars, moons or comets. The explorer may carry appropriate sensors and instruments to evaluate the composition, structure, mineralogy and possible biology of the subsurface medium, as well as perhaps returning samples of that medium back to the surface. The exploration capability of the SSX enables scientific research and resource exploration which may not be possible or may be prohibitively expensive by alternative means such as conventional drilling.
The SSX is a relatively small robotic vehicle capable of penetrating underground, through soil, rock, or mixtures thereof, to depths many times deeper than would be possible using conventional drilling techniques of comparable mass and power. This is possible because the vehicle excavates material ahead of it""s travel, moves it only a short distance to the rear of the vehicle, and recompacts it behind the vehicle. The excavated and recompacted material may also be called xe2x80x9coverburden.xe2x80x9d Unlike prior art systems, with the present invention, the vehicle itself is compact and essentially self-contained, with power delivered to it over a fine tether which is paid out from the vehicle and becomes embedded in the recompacted medium behind the vehicle as it progresses.
One of the oldest techniques for excavation of compacted soil and rock is percussion, or hammering. Hammering of rock causes a network of fine cracks to form ahead of the hammer in zones where the compressive strength of the material is exceeded. These cracks interlock under repeated blows to ultimately create from the rock a collection of particles. In the absence of any active mechanism to remove the particles, they are ground into a fine powder. This powder can flow in a fashion similar to a fluid around the SSX as it advances, especially under the extreme acoustic excitation of the hammering action. Thus a simple, perhaps the simplest, mechanism for excavating the subsurface medium is to have an internal hammer mechanism in the SSX. In short, the SSX can be a self-contained pile driver.
The hammer mechanism of the SSX is preferably contained within the body of the SSX, which should be sealed against intrusion of dust generated by the percussive action. It should have a free volume in which to accelerate the hammer. Thus, the front end of the vehicle should not be the hammer mechanism itself, but instead may be an intermediate material which seals the front of an acceleration volume and transmits the percussive shock from the hammer to the surrounding medium. This front portion can be called a xe2x80x9cchisel,xe2x80x9d also referred to herein as a nose piece. The hammer impacts the chisel, which in turn imparts forces on the medium which are large compared to the compressive strength of the terrain material. The momentum of the hammer is conserved with the hammer-chisel assembly, depending somewhat on the amount of rebound in the hammer from the chisel. In the case of zero rebound, the final kinetic energy of the hammer-chisel assembly is equal to the initial kinetic energy of the hammer times the ratio of the hammer mass to the combined hammer-chisel mass. This ratio becomes adverse if the chisel becomes massive. To achieve good energy transfer from the hammer to the chisel, the hammer should be made as massive as possible, and the nose and shell should be as light as possible.
The hammer mechanism may comprise a hammer portion, used as a flywheel, rotated to high surface speeds. A non-uniform pitch thread on an intermediate shaft is used to convert the rotational motion to linear motion for the hammer portion, which in turn imparts force to a nose piece which pommels the material in front of the nose piece, causing vibrational exitation of the material thereby fracturing the material.